设置textField的placeholder字体的颜色，默认是灰色
//设置textField的placeholder字体的颜色，默认是灰色
UIColor *color = [UIColor whiteColor];
UIColor *color = [UIColor whiteColor];
self.loginNumText.attributedPlaceholder = [[NSAttributedString alloc] initWithString:@"请输入用户名" attributes:@{NSForegroundColorAttributeName: color}];